Journal of Neuroscience, Vol 4, 741-750, Copyright © 1984 by Society for Neuroscience
Effects of iontophoretically released peptides on primate spinothalamic tract cells
WS Willcockson, JM Chung, Y Hori, KH Lee and WD Willis
The peptides substance P (SP), methionine-enkephalin (M-ENK), leucine-
enkephalin (L-ENK), and cholecystokinin (CCK) were released
iontophoretically near spinothalamic tract (STT) cells in anesthetized
monkeys and STT-like cells in decorticate, spinalized monkeys. Peptide
effects were observed on background discharges, firing induced by release
of glutamate, and activity evoked by pinching the skin. SP could have any
of several actions on STT cells, including excitation, inhibition, or
biphasic effects. Multiple effects often resulted while recording from an
individual cell when the dose or the electrode position was changed. M-ENK
and L-ENK generally inhibited STT cells, and in some cases it was possible
to demonstrate a reversal of the inhibition by naloxone. CCK also caused an
inhibition that was additive with that produced by L-ENK. The multiple
actions of SP on STT cells suggests the possibility that there may be more
than one type of SP receptor on STT cells, although alternative
explanations should be considered. Inhibition of STT cells by M- and L-ENK
is consistent with the known analgesic action of opiates through spinal
cord mechanisms. CCK has an action on STT cells similar to that of the
enkephalins.